This invention relates to a color separation/synthetic optical system using dichroic mirrors used in a liquid crystal projection television, etc., and more particularly to a color separation/synthetic optical system constructed to reduce an astigmatism produced in a light transmitted through dichroic mirrors arranged in an inclined manner.
The color separation optical system for separating a white light into three colors of red, green and blue by using dichroic mirrors and/or a color synthetic optical system for synthesizing rays of light of three colors of red, green and blue by using the same are employed in a liquid crystal projection television, a color television, etc..
Generally, a color separation/synthetic optical system is of a structure such that a plurality of dichroic mirrors for allowing any one of rays of light in respective wavelength bands of red, green and blue to be transmitted therethrough or to be reflected thereon are successively provided in parallel with each other in a manner inclined with respect to an optical axis, and a liquid crystal panel is arranged on the light emitting side of each dichroic mirror. Rays of color light of red, green and blue separated by the respective dichroic mirrors are incident on a liquid crystal panel, and are transmitted through an image portion corresponding to respective rays of color light. Thus, these rays of color light are color-separated. Further, respective rays of color light transmitted through the liquid crystal panel are synthesized at an optical system such as a mirror, etc. provided close to a color separation system. When synthesized respective rays of color light are projected onto a display plane such as a screen, etc., a color projected image is provided.
However, in the separation of respective rays of light by the dichroic mirror, since separation into respective rays of color light of red, green and blue by the reflection/transmission on and through the dichroic mirror is carried out, there would occur an astigmatism with respect to a light in the wavelength band transmitted, disadvantageously failing to provide a distinct projected image.